From the 802.11n VRD - http://www.arubanetworks.com/vrd/80211nNetworksVRD/wwhelp/wwhimpl/js/html/wwhelp.htm
LAN Edge and Core
The LAN that is between the AP and the mobility controller must recognize and prioritize DCSP-marked traffic through the network. When in tunnel or decrypt-tunnel mode, the AP translates WMM marks into DSCP marks and places them in the GRE header so that the intervening network properly prioritizes traffic. Similarly, the core must respect the QoS marks from the mobility controller to the multimedia servers.
It is critical that all devices in the network be capable of and configured for QoS support. Switches and the multimedia servers themselves should mark traffic appropriately. Failure to ensure end-to-end prioritization can result in unpredictable performance for these applications.